Because of the increasing worldwide demand for energy, and the consequent depletion of nonrenewable resources, increasingly greater usage is being made of solar energy. Photovoltaic devices are attractive sources of power insofar as they are relatively compact, silent, nonpolluting and consume no expendable natural resources in their operation.
Solar photovoltaic energy sources are particularly attractive in those areas or under those conditions where power-grid supplied electricity is unavailable. Solar photovoltaic power is used in military and aerospace applications, in agricultural applications, in developing nations and by persons engaged in recreational pursuits such as camping, boating, mountain climbing and the like.
Single crystal photovoltaic devices, especially silicon photovoltaic devices have been utilized for some time as sources of electrical power. However, the utility of such devices is limited by problems associated with their manufacture. More particularly, single crystal materials (1) are difficult to produce in sizes substantially larger than several inches in diameter, (2) are relatively thick and heavy; and (3) are expensive and time consuming to fabricate. Consequently, single crystal photovoltaic power modules are limited in use by cost, bulk and fragility; accordingly, there is a need for a source of solar photovoltaic power which is rugged, reliable, readily transportable and low in cost.
Recently, considerable efforts have been made to develop processes for depositing amorphous semiconductor films, each of which can encompass relatively large areas, and which can be doped to form p-type and n-type materials for the production of p-i-n type devices substantially equivalent to those produced by their crystalline counterparts. It is to be noted that the term "amorphous" as used herein, includes all materials or alloys which have long range disorder, although they may have short or intermediate range order or even contain, at times, crystalline inclusions.
It is now possible to prepare by glow discharge or other vapor deposition techniques, thin film amorphous silicon or germanium based alloys in large areas, said alloys possessing acceptable concentrations of localized states in the energy gaps thereof and high quality electronic properties. Suitable techniques for the preparation of such alloys are fully described in U.S. Pat. No. 4,226,898, entitled "Amorphous Semiconductor Equivalent to Crystalline Semiconductors," of Stanford R. Ovshinsky and Arun Madan which issued Oct. 7, 1980 and in U.S. Pat. No. 4,217,374, under the same title, which issued on Aug. 12, 1980, to Stanford R. Ovshinky and Masatsugu Izu, and in U.S. Pat. No. 4,504,518 of Stanford R. Ovshinsky, David D. Allred, Lee Walter and Stephen J. Hudgens entitled "Method of Making Amorphous Semiconductor Alloys and Devices Using Microwave Energy," which issued on Mar. 12, 1985, and in U.S. Pat. No. 4,517,223 under the same title which issued on May 14, 1985 to Stanford R. Ovshinsky, David D. Allred, Lee Walter and Steven J. Hudgens, the disclosures of which are incorporated herein by reference. As disclosed in these patents, it is believed that fluorine introduced into the amorphous semiconductor operates to substantially reduce the density of the localized states therein and facilitates the addition of other alloying materials.
It is of obvious commercial importance to be able to mass produce photovoltaic devices such as solar cells. However, with crystalline cells, mass production was limited to batch processing techniques by the inherent growth requirements of the crystals. Unlike crystalline silicon, amorphous silicon and germanium alloys can be deposited in multiple layers over large area substrates to form solar cells in a high volume, continuous processing system. Such continuous processing systems are disclosed in the following U.S. Pat. Nos. 4,400,409, for A Method of Making P-Doped Silicon Films And Devices Made Therefrom; No. 4,410,588, for Continuous Amorphous Solar Cell Deposition And Isolation System And Method; U.S. Pat. No. 4,547,711, for Continuous Systems For Depositing Amorphous Semiconductor Material; U.S. Pat. No. 4,492,181 for Method And Apparatus For Continuously Producing Tandem Amorphous Photovoltaic Cells; and U.S. Pat. No. 4,485,125 for Method And Apparatus For Continuously Producing Tandem Amorphous Photovoltaic Cells. As disclosed in these patents the disclosures of which are incorporated herein by reference, a substrate may be continuously advanced through a succession of deposition chambers, wherein each chamber is dedicated to the deposition of a specific semiconductor material. In making a solar cell of n-i-p type configuration, the first chamber is dedicated for depositing a n-type amorphous silicon alloy, the second chamber is dedicated for depositing an intrinsic amorphous silicon alloy, and the third chamber is dedicated for depositing a p-type amorphous silicon alloy.
Since each deposited semiconductor alloy, and especially the intrinsic semiconductor alloy, must be of high purity; (1) the deposition environment in the intrinsic deposition chamber is isolated, by specially designed gas gates, from the doping constituents within the other chambers to prevent the diffusion of doping constituents into the intrinsic chamber; (2) the substrate is carefully cleansed prior to initiation of the deposition process to remove contaminants; (3) all of the chambers which combine to form the deposition apparatus are sealed and leak checked to prevent the influx of environmental contaminants; (4) the deposition apparatus is pumped down and flushed with a sweep gas to remove contaminants from the interior walls thereof; and (5) only the purest reaction gases are employed to form the deposited semiconductor materials. In other words, every possible precaution is taken to insure that the sanctity of the vacuum envelope formed by the various chambers of the deposition apparatus remains uncontaminated by impurities, regardless of origin.
The layers of semiconductor material thus deposited in the vacuum envelope of the deposition apparatus may be utilized to form a photovoltaic device including one or more p-i-n cells, one or more n-i-p cells, a Schottky barrier, as well as photodiodes, phototransistors, or the like. Additionally, by making multiple passes through the succession of deposition chambers, or by providing an additional array of deposition chambers, multiple stacked cells of various configurations may be obtained. By the use of a flexible substrate in the deposition process, large area, flexible photovoltaic devices may be fabricated.
The large area semiconductor material thus produced may be used as a single large area photovoltaic cell or may be configured into a variety of smaller area photovoltaic cells as well as modules comprised of arrays of interconnected smaller area devices. For example, as disclosed in U.S. Pat. No. 4,514,579 of Joseph J. Hanak entitled "Large Area Photovoltaic Cell and Method for Producing Same" the disclosure of which is incorporated herein by reference, a large area photovoltaic cell tolerant of defects in or damage to smaller area portions thereof may be produced by interconnecting a plurality of smaller area cells in a mixed series-parallel relationship.
The assignee of the instant invention has also developed techniques for sequentially depositing layers of semiconductor material upon a very thin, flexible substrate material so as to allow for the manufacture of "ultralight" photovoltaic cells and modules manifesting extemely high power to weight ratios. Such techniques are disclosed in U.S. patent application Ser. No. 913,046, now abandoned, a division of U.S. patent application serial No. 696,390 filed Jan. 30, 1985 and entitled "Extremely Lightweight, Flexible Semiconductor Device Arrays and Method of Making Same," the disclosure of which is incorporated herein by reference. Since it is now possible to manufacture lightweight and ultralightweight flexible solar cell power sources, it would be highly advantageous to incorporate such solar cell power sources into modules, which modules have been specifically adapted for ease of portability and rapid deployment.
Heretofore, photovoltaic cells were generally made of single crystal material and accordingly were bulky, brittle and expensive. Even thin film materials presented problems in the fabrication of large area stowable modules insofar as most of said prior art thin film photovoltaic devices were deposited upon glass or rigid metal substrates. However, the present ability to manufacture photovoltaic cells upon lightweight flexible substrates now allows for the manufacture of modules which may be rolled up or otherwise compacted for storage.
While modules configured according to the aforedescribed prior art may be rolled into a cylindrical configuration, the ultimate size of these stowed modules is still limited by the fact that compact folding of the photovoltaic material frequently presents problems. In cases where the material is deposited upon a thin metal substrate, folding is not possible because the substrate itself would become kinked or creased and would ultimately crack. Photovoltaic devices deposited upon ultrathin substrates do allow for some very limited degree of folding. However, if the device is folded around too sharp a radius or if the folded module is rolled too tightly, the substrate will take a permanent crease or the photovoltaic layers may be cracked.
In some instances the length of the rolled up module will not present problems, such as for example when a relatively large amount of space is available for its storage or in those instances where a relatively narrow module is being stored. However, in many instances it would be highly desirable to fold a large area photovoltaic module so as to store it in as compact a container as possible. Additionally, it is highly desirable to be able to quickly and simply deploy the module when power is needed.
The instant invention provides for a large area solar power module which may be readily folded and rolled without causing any damage thereto so as to allow for the very compact storage thereof. Additionally, the module of the instant invention may include a lightweight support member such as a flexible framework for supporting the module and orienting it so as to receive solar radiation. The module may also include a storage container for protecting the power generating module and the support framework when not in use.
According to the principles disclosed herein which will be described in greater detail below, a large area module is formed of a plurality of solar power panels hingedly interconnected so as to allow for the ready folding thereof. While hinges have been known and used in one form or another since time immemorial, most hinges are not flexible enough to allow for rolling of folded material. While relatively flexible hinges formed of polymeric materials such as polypropylene are presently available, such hinges are not suitable for the manufacture of hinged, portable solar power modules since they retain the hinged members in relatively rigid alignment.
Use of such heretofore available hinges in the manufacture of a rollable, foldable solar power module presents a problem of buckling since the stacked, folded photovoltaic panels to the interior of the roll are bending about a smaller radius than are the panels to the exterior of the roll. The differential radii necessitate a slippage of the layers past one another to allow for smooth rolling, and if this slippage is prevented by the presence of a rigid hinge, buckling, tearing or other damage can result.
The instant invention overcomes these problems by providing a large area photovoltaic module comprised of a plurality of large area solar panels interconnected by a hinge which allows for folding of the panels atop one another and also allows for relative planar displacement of adjoining panels so that slippage may be provided for when the module is rolled. In this manner, the large area module of the instant invention may be readily rolled to a fairly small radius for storage and may be rapidly unrolled and unfolded for deployment.
These and other advantages and features of the instant invention will be more apparent from the brief description, the drawings, the detailed description of the drawings and the claims which follow.